How to Use Spinners

Spinners are similar to combo boxes and lists in that they let the user choose from a range of values. Like editable combo boxes, spinners allow the user to type in a value. Unlike combo boxes, spinners do not have a drop-down list that can cover up other components. Because spinners do not display possible values — only the current value is visible — they are often used instead of combo boxes or lists when the set of possible values is extremely large. However, spinners should only be used when the possible values and their sequence are obvious.

A spinner is a compound component with three subcomponents: two small buttons and an editor. The editor can be any JComponent, but by default it is implemented as a panel that contains a formatted text field. The spinner's possible and current values are managed by its model.

Here is a picture of an application named SpinnerDemo that has three spinners used to specify dates:

The code for the main class can be found in SpinnerDemo.java. The Month spinner displays the name of the first month in the user's locale. The possible values for this spinner are specified using an array of strings. The Year spinner displays one value of a range of integers, initialized to the current year. The Another Date spinner displays one value in a range of Date objects (initially the current date) in a custom format that shows just a month and year.

To create a spinner, first create its model and then pass the model into the JSpinner constructor. For example:

String[] monthStrings = getMonthStrings(); //get month names
SpinnerListModel monthModel = new SpinnerListModel(monthStrings);
JSpinner spinner = new JSpinner(monthModel);

The rest of this section covers the following topics:

• Using Standard Spinner Models and Editors
• Specifying Spinner Formatting
• Creating Custom Spinner Models and Editors
• Detecting Spinner Value Changes
• The Spinner API
• Examples That Use Spinners

Using Standard Spinner Models and Editors

The Swing API provides three spinner models:

SpinnerListModel

The SpinnerListModel is a model whose values are defined by an array of objects or a List object. The Month spinner in the SpinnerDemo example uses this model, initialized with an array derived from the value returned by the getMonths method of the java.text.DateFormatSymbols class. See SpinnerDemo.java for details.

SpinnerNumberModel

The SpinnerNumberModel supports sequences of numbers which can be expressed as double objects, int objects, or Number objects. You can specify the minimum and maximum allowable values, as well as the step size — the amount of each increment or decrement. The Year spinner uses this model, created with the following code:

SpinnerModel model =
        new SpinnerNumberModel(currentYear, //initial value
                               currentYear - 100, //min
                               currentYear + 100, //max
                               1);                //step

SpinnerDateModel

The SpinnerDateModel supports sequences of Date objects. You can specify the minimum and maximum dates, as well as the field (such as Calendar.YEAR) to increment or decrement. Note, however, that some types of look and feel ignore the specified field, and instead change the field that appears selected. The Another Date spinner uses this model, created with the following code:

Date initDate = calendar.getTime();
calendar.add(Calendar.YEAR, -100);
Date earliestDate = calendar.getTime();
calendar.add(Calendar.YEAR, 200);
Date latestDate = calendar.getTime();
model = new SpinnerDateModel(initDate,
                             earliestDate,
                             latestDate,
                             Calendar.YEAR);

When you set the spinner's model, the spinner's editor is automatically set. The Swing API provides an editor class corresponding to each of the three model classes listed above. These classes — JSpinner.ListEditor, JSpinner.NumberEditor, and JSpinner.DateEditor — are all subclasses of the JSpinner.DefaultEditor class that feature editable formatted text fields. If you use a model that does not have an editor associated with it, the editor is by default a JSpinner.DefaultEditor instance with a non-editable formatted text field.

Specifying Spinner Formatting

To change the formatting used in a standard spinner editor, you can create and set the editor yourself.

The JSpinner.NumberEditor and JSpinner.DateEditor classes have constructors that allow you to create an editor that formats its data in a particular way. For example, the following code sets up the Another Date spinner so that instead of using the default date format, which is long and includes the time, it shows just a month and year in a compact way.

spinner.setEditor(new JSpinner.DateEditor(spinner, "MM/yyyy"));

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Note: 

You can play with date formats by running ComboBoxDemo2 example. Click the Launch button to run ComboBoxDemo2 using Java™ Web Start (download JDK 6 or later). Alternatively, to compile and run the example yourself, consult the example index.

For information about format strings, see the Formatting lesson of the Internationalization trail.

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To change the formatting when using a default editor, you can obtain the editor's formatted text field and invoke methods on it. You can call those methods using the getTextField method defined in the JSpinner.DefaultEditor class. Note that the Swing-provided editors are not formatted text fields. Instead, they are the JPanel instances that contain a formatted text field. Here is an example of getting and invoking methods on the editor's formatted text field:

//Tweak the spinner's formatted text field.
ftf = getTextField(spinner);
if (ftf != null ) {
    ftf.setColumns(8); //specify more width than we need
    ftf.setHorizontalAlignment(JTextField.RIGHT);
}
...

public JFormattedTextField getTextField(JSpinner spinner) {
    JComponent editor = spinner.getEditor();
    if (editor instanceof JSpinner.DefaultEditor) {
        return ((JSpinner.DefaultEditor)editor).getTextField();
    } else {
        System.err.println("Unexpected editor type: "
                           + spinner.getEditor().getClass()
                           + " isn't a descendant of DefaultEditor");
        return null;
    }
}

Creating Custom Spinner Models and Editors

If the existing spinner models or editors do not meet your needs, you can create your own.

The easiest route to creating a custom spinner model is to create a subclass of an existing AbstractSpinnerModel subclass that already does most of what you need. An alternative is to implement your own class by extending AbstractSpinnerModel class, which implements the event notifications required for all spinner models.

The following subclass of SpinnerListModel implements a spinner model that cycles through an array of objects. It also lets you specify a second spinner model that will be updated whenever the cycle begins again. For example, if the array of objects is a list of months, the linked model could be for a spinner that displays the year. When the month flips over from December to January the year is incremented. Similarly, when the month flips back from January to December the year is decremented.

public class CyclingSpinnerListModel extends SpinnerListModel {
    Object firstValue, lastValue;
    SpinnerModel linkedModel = null;

    public CyclingSpinnerListModel(Object[] values) {
        super(values);
        firstValue = values[0];
        lastValue = values[values.length - 1];
    }

    public void setLinkedModel(SpinnerModel linkedModel) {
        this.linkedModel = linkedModel;
    }

    public Object getNextValue() {
        Object value = super.getNextValue();
        if (value == null) {
            value = firstValue;
            if (linkedModel != null) {
                linkedModel.setValue(linkedModel.getNextValue());
            }
        }
        return value;
    }

    public Object getPreviousValue() {
        Object value = super.getPreviousValue();
        if (value == null) {
            value = lastValue;
            if (linkedModel != null) {
                linkedModel.setValue(linkedModel.getPreviousValue());
            }
        }
        return value;
    }
}

The CyclingSpinnerListModel model is used for the Month spinner in the SpinnerDemo2 example, an example that is almost identical to the SpinnerDemo. Click the Launch button to run SpinnerDemo2 using Java™ Web Start (download JDK 6 or later). Alternatively, to compile and run the example yourself, consult the example index.

As we mentioned before, if you implement a spinner model that does not descend from SpinnerListModel, SpinnerNumberModel, or SpinnerDateModel, then the spinner's default editor is a non-editable instance of JSpinner.DefaultEditor. As you have already seen, you can set a spinner's editor by invoking the setEditor method on the spinner after the spinner's model property has been set. An alternative to using setEditor is to create a subclass of the JSpinner class and override its createEditor method so that it returns a particular kind of editor whenever the spinner model is of a certain type.

In theory at least, you can use any JComponent instance as an editor. Possibilities include using a subclass of a standard component such as JLabel, or a component you have implemented from scratch, or a subclass of JSpinner.DefaultEditor. The only requirements are that the editor must be updated to reflect changes in the spinner's value, and it must have a reasonable preferred size. The editor should generally also set its tool tip text to whatever tool tip text has been specified for the spinner. An example of implementing an editor is provided in the next section.

Detecting Spinner Value Changes

You can detect that a spinner's value has changed by registering a change listener on either the spinner or its model. Here is an example of implementing such a change listener. This example is from SpinnerDemo3, which is based on SpinnerDemo and uses a change listener to change the color of some text to match the value of the Another Date spinner. Click the Launch button to run SpinnerDemo3 using Java™ Web Start (download JDK 6 or later). Alternatively, to compile and run the example yourself, consult the example index.

public class SpinnerDemo3 extends JPanel
                          implements ChangeListener {
    protected Calendar calendar;
    protected JSpinner dateSpinner;
    ...
    public SpinnerDemo3() {
        ...
        SpinnerDateModel dateModel = ...;
        ...
        setSeasonalColor(dateModel.getDate()); //initialize color

        //Listen for changes on the date spinner.
        dateSpinner.addChangeListener(this);
        ...
    }

    public void stateChanged(ChangeEvent e) {
        SpinnerModel dateModel = dateSpinner.getModel();
        if (dateModel instanceof SpinnerDateModel) {
            setSeasonalColor(((SpinnerDateModel)dateModel).getDate());
        }
    }

    protected void setSeasonalColor(Date date) {
        calendar.setTime(date);
        int month = calendar.get(Calendar.MONTH);
        JFormattedTextField ftf = getTextField(dateSpinner);
        if (ftf == null) return;

        //Set the color to match northern hemisphere seasonal conventions.
        switch (month) {
            case 2:  //March
            case 3:  //April
            case 4:  //May
                     ftf.setForeground(SPRING_COLOR);
                     break;
            ...
            default: //December, January, February
                     ftf.setForeground(WINTER_COLOR);
        }
    }
    ...
}

The following example implements an editor which has a change listener so that it can reflect the spinner's current value. This particular editor displays a solid color of gray, ranging anywhere from white to black. Click the Launch button to run SpinnerDemo4 using Java™ Web Start (download JDK 6 or later). Alternatively, to compile and run the example yourself, consult the example index.

...//Where the components are created:
JSpinner spinner = new JSpinner(new GrayModel(170));
spinner.setEditor(new GrayEditor(spinner));

class GrayModel extends SpinnerNumberModel {
    ...
}

class GrayEditor extends JLabel
                 implements ChangeListener {
    public GrayEditor(JSpinner spinner) {
        setOpaque(true);
        ...
        //Get info from the model.
        GrayModel myModel = (GrayModel)(spinner.getModel());
        setBackground(myModel.getColor());
        spinner.addChangeListener(this);
        ...
        updateToolTipText(spinner);
    }

    protected void updateToolTipText(JSpinner spinner) {
        String toolTipText = spinner.getToolTipText();
        if (toolTipText != null) {
            //JSpinner has tool tip text.  Use it.
            if (!toolTipText.equals(getToolTipText())) {
                setToolTipText(toolTipText);
            }
        } else {
            //Define our own tool tip text.
            GrayModel myModel = (GrayModel)(spinner.getModel());
            int rgb = myModel.getIntValue();
            setToolTipText("(" + rgb + "," + rgb + "," + rgb + ")");
        }
    }

    public void stateChanged(ChangeEvent e) {
            JSpinner mySpinner = (JSpinner)(e.getSource());
            GrayModel myModel = (GrayModel)(mySpinner.getModel());
            setBackground(myModel.getColor());
            updateToolTipText(mySpinner);
    }
}

The Spinner API

The following tables list some of the commonly used API for using spinners. If you need to deal directly with the editor's formatted text field, you should also see The FormattedTextField API. Other methods you might use are listed in the API tables in The JComponent Class.

• Classes Related to Spinners
• Useful JSpinner Constructors and Methods
• Useful Editor Constructors and Methods
• SpinnerListModel Methods
• SpinnerDateModel Methods
• SpinnerNumberModel Methods

Examples That Use Spinners

This table lists examples that use spinners and points to where those examples are described.